The present disclosure pertains to the field of information processing, and more particularly, to the field of handling interrupts in a virtualization environment.
Generally, the concept of virtualization in information processing systems allows multiple instances of one or more operating systems (each, an “OS”) to run on a single information processing system, even though each OS is designed to have complete, direct control over the system and its resources. Virtualization is typically implemented by using software (e.g., a virtual machine monitor, or a “VMM”) to present to each OS a “virtual machine” (“VM”) having virtual resources, including one or more virtual processors, that the OS may completely and directly control, while the VMM maintains a system environment for implementing virtualization policies such as sharing and/or allocating the physical resources among the VMs (the “virtualization environment”). Each OS, and any other software, that runs on a VM is referred to as a “guest” or as “guest software,” while a “host” or “host software” is software, such as a VMM, that runs outside of, and may or may not be aware of, the virtualization environment.
A physical processor in an information processing system may support virtualization, for example, by supporting an instruction to enter a virtualization environment to run a guest on a virtual processor (i.e., a physical processor under constraints imposed by a VMM) in a VM. In the virtualization environment, certain events, operations, and situations, such as external interrupts or attempts to access privileged registers or resources, may be “intercepted,” i.e., cause the processor to exit the virtualization environment so that a VMM may operate, for example, to implement virtualization policies. A physical processor may also support other instructions for maintaining a virtualization environment, and may include memory or register bits that indicate or control virtualization capabilities of the physical processor.
A physical processor supporting a virtualization environment may receive an interrupt request while a guest is running on a virtual processor within the virtual environment. Typically, the interrupt request would be intercepted and control would be transferred to a VMM to determine how to handle the interrupt. For example, an interrupt service routine may be called by the VMM, or the VMM may create a virtual interrupt and inject it into a VM to allow a guest to call an interrupt service routine. In many cases, the VM that is entered to call the interrupt service request may be the same VM that was exited to allow the VMM to intercept the interrupt request. For example, the interrupt request may have been generated by an input/output (“I/O”) device assigned to the same VM that was exited, or an interrupt request may be an inter-processor interrupt between two virtual processors in the same VM.